LEDs are well-known solid state devices that can generate light having a peak wavelength in a specific region of the visible spectrum. LEDs are widely used as illuminators, indicators and displays due to their fast response time, high color saturation, and long life.
Referring to FIG. 7, a related art LED 10 includes a substrate 11, an LED chip 12, two conducting wires 13, a first electrode 14, a second electrode 15, a first connecting pin 16, a second connecting pin 17, and a transparent sealant 18.
The substrate 11 includes an upper surface 111 and a lower surface 112. The first electrode 14, the second electrode 15, and the LED chip 12 are symmetrically formed on the upper surface 111 of the substrate 11, wherein the first electrode 14 and the second electrode 15 are respectively located at two opposite sides of the LED chip 12.
One of the two conducting wires 13 interconnects the LED chip 12 and the first electrode 14, and the other conducting wire 13 interconnects the LED chip 12 and the second electrode 15. The first connecting pin 16 passes through the substrate 11. One end of the first connecting pin 16 is connected to the first electrode 14, and the other end of the first connecting pin 16 protrudes out from the lower surface 112 of the substrate 11. The second connecting pin 17 also passes through the substrate 11. One end of the second connecting pin 17 is connected to the second electrode 15, and the other end of the second connecting pin 17 protrudes out from the lower surface 112 of the substrate 11.
The sealant 18 is formed on the upper surface 111 of the substrate 11 and covers the first electrode 14, the second electrode 15, and the LED chip 12. The sealant 18 includes a plurality of phosphor particles 181 therein. The LED chip 12 is a blue LED chip which emits blue light. The phosphor particles 181 may be yttrium aluminum garnet (YAG).
When an operation voltage is provided between the first connecting pin 16 and the second connecting pin 17, the operation voltage across the LED chip 12 makes the LED chip 12 emit blue light. Some of the blue light illuminates the phosphor particles 181 thereby causing the phosphor particles 181 to emit yellow light. The blue light mixed with the yellow light forms white light.
In manufacture of the LED 10, the sealant 18 is initially in a non-solid state prior to being heated and solidified. During this time, the LED 10 may be placed somewhere such as at a workstation for a relatively long time. As a result, the phosphor particles 181 in the sealant 18 are liable to slowly drift down to positions adjacent to the upper surface 111 of the substrate 11 due to the effects of gravity. When this happens, a distribution of the phosphor particles 181 is uneven along vertical directions. In operation of the LED 10, the uneven distribution of the phosphor particles 181 results in uneven transmission of the blue light through the sealant 18, and the chroma of the white light formed by the mixed blue light and yellow light varies with different viewing angles.
It is desired to provide a new LED which can overcome the described limitations.